Aza-cyanoquinolinone pde9 inhibitors

ABSTRACT

The present invention is directed to azacyanoquinolinone compounds which may be useful as therapeutic agents for the treatment of central nervous system disorders associated with phosphodiesterase 9 (PDE9). The present invention also relates to the use of such compounds for treating neurological and psychiatric disorders, such as schizophrenia, psychosis or Huntington&#39;s disease, and those associated with striatal hypofunction or basal ganglia dysfunction.

FIELD OF THE INVENTION

The invention relates generally to compounds which act as inhibitors of the phosphodiesterase (PDE) 9 enzyme, compositions and therapeutic uses thereof.

BACKGROUND OF THE INVENTION

Schizophrenia is a debilitating disorder affecting the psychic and motor functions of the brain. It is typically diagnosed in individuals in their early to mid-twenties and symptoms include hallucinations and delusions or at the other extreme, anhedonia or social withdrawal. Across the spectrum, the symptoms are indicative of cognitive impairment and functional disabilities. Notwithstanding improvements in antipsychotic treatments, current therapies, including typical (haloperidol) and atypical (clozapine or olanzapine) antipsychotics, have been less than acceptable and result in an extremely high rate of noncompliance or discontinuation of medication. Dissatisfaction with therapy is attributed to lack of efficacy or intolerable and unacceptable side affects. The side effects have been associated with significant metabolic, extrapyramidal, prolactic and cardiac adverse events (Lieberman et al., N. Engl. J. Med. (2005) 353:1209-1223).

While multiple pathways are believed to be involved with the pathogenesis of schizophrenia leading to psychosis and cognition deficits, much attention has focused on the role of glutamate/NMDA dysfunction associated with cyclic guanosine monophosphate (cGMP) levels and the dopaminergic D2 receptor associated with cyclic adenosine monophosphate (cAMP). These ubiquitous second messengers may be responsible for altering the function of many intracellular proteins. Cyclic AMP is thought to regulate the activity of cAMP-dependent protein kinase (PKA), which in turns phosphorylates and regulates many types of proteins including ion channels, enzymes and transcription factors. Similarly, cGMP may also be responsible for downstream regulation of kinases and ion channels.

One pathway for affecting the levels of cyclic nucleotides, such as cAMP and cGMP, is to alter or regulate the enzymes that degrade these enzymes, known as 3′, 5′-cyclic nucleotide specific phosphodiesterases (PDEs). The PDE superfamily includes twenty one genes that encode for eleven families of PDEs. These families are further subdivided based on catalytic domain homology and substrate specificity and include the: (1) cAMP specific, PDE4A-D, 7A and 7B, and 8A and 8B; (2) cGMP specific, PDE 5A, 6A-C, and 9A; and (3) those that are dual substrate, PDE 1A-C, 2A, 3A and 3B, 10A, and 11A. The homology between the families, ranging from 20% to 45% suggests that it may be possible to develop selective inhibitors for each of these subtypes.

The identification of PDE9 was recently reported and was distinguished from other PDEs on the basis of its amino acid sequence, functional properties, and tissue distribution (Fisher et al., J Biol Chem., 1998, 273(25): 15559-64). PDE9V is encoded by two genes (PDE9A and PDE9B) and is cGMP specific. To date, at least 20 different splice variants have been discovered (PDE9A1-PD9A20) in human and in mouse (Guipponi et al., Hum. Genet., 1998, 103(4): 386-92). Structural study of PDE9A have been shown that its cDNA of the different splice variants share a high percentage of amino acid identity in the catalytic domain (Rentero et al., Biochem. Biophys. Res. Commun, 2003, 301(3): 686-92). However, despite its highest specificity for cGMP among all the PDEs, PDE9A lacks a GAF domain, whose binding of cGMP usually activates catalytic activity. Besides its expression in the kidney, spleen, and other peripheral organs, PDE9 is widespread through the brain in mice, rats and humans with high similarities of expression in striatum, cerebellum, olfactory bulbs, amygdala and midbrain (van Staveren et al., J Neurocytol 2002, 31(8-9): 729-41). The expression is mainly detected in neurons and astrocytes.

Inhibition of PDE9 is believed to be useful in the treatment of cognitive deficit associated with neurodegenerative and psychiatric disorders and a wide variety of conditions or disorders that would benefit from increasing levels of cGMP within neurons, including Alzheimer's disease, schizophrenia, and depression.

SUMMARY OF THE INVENTION

The present invention is directed to azacyanoquinolinone compounds which may be useful as therapeutic agents for the treatment of central nervous system disorders associated with phosphodiesterase 9 (PDE9). The present invention also relates to the use of such compounds for treating neurological and psychiatric disorders, such as schizophrenia, psychosis or Huntington's disease, and those associated with striatal hypofunction or basal ganglia dysfunction.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is directed to compounds of the formula I:

wherein: R⁵ is selected from the group consisting of:

(1) hydrogen, and

(2) —C₁₋₆alkyl;

R⁶ is —C₁₋₆alkyl, which is unsubstituted or substituted with oxetane; or R⁵ and R⁶ are joined together with a —C₃₋₆alkyl through the nitrogen atom to which they are attached to form a azetidine, pyrrolidine, piperidine, or azepan ring, which is unsubstituted or substituted with pyrazole or one or two —C₁₋₆alkyl; or a pharmaceutically acceptable salt thereof.

An embodiment of the present invention includes compounds wherein

R⁵ is selected from the group consisting of:

(1) hydrogen, and

(2) ethyl.

An embodiment of the present invention includes compounds wherein

R⁶ is ethyl, which is unsubstituted or substituted with oxetane.

An embodiment of the present invention includes compounds wherein

R⁵ and R⁶ are joined together with a —C₃₋₆alkyl through the nitrogen atom to which they are attached to form a azetidine, pyrrolidine, piperidine, or azepan ring, which is unsubstituted or substituted with pyrazole or one or two —C₁₋₆alkyl.

An embodiment of the present invention includes compounds herein, other than the compound: (R)-4-(3-[1H-pyrazol-1-yl]pyrrolidin-1-yl)-2-oxo-1,2-dihydroquinoline-3-carbonitrile.

An embodiment of the present invention includes compounds herein, other than the compound: 4-(azepan-1-yl)-2-oxo-1,2-dihydroquinoline-3-carbonitrile.

Certain embodiments of the present invention include a compound which is selected from the group consisting of the subject compounds of the Examples herein or a pharmaceutically acceptable salt thereof.

The compounds of the present invention may contain one or more asymmetric centers and can thus occur as racemates and racemic mixtures, single enantiomers, diastereomeric mixtures and individual diastereomers. Additional asymmetric centers may be present depending upon the nature of the various substituents on the molecule. Each such asymmetric center will independently produce two optical isomers and it is intended that all of the possible optical isomers and diastereomers in mixtures and as pure or partially purified compounds are included within the ambit of this invention. The present invention is meant to comprehend all such isomeric forms of these compounds. Formula I shows the structure of the class of compounds without specific stereochemistry.

The independent syntheses of these diastereomers or their chromatographic separations may be achieved as known in the art by appropriate modification of the methodology disclosed herein. Their absolute stereochemistry may be determined by the x-ray crystallography of crystalline products or crystalline intermediates which are derivatized, if necessary, with a reagent containing an asymmetric center of known absolute configuration. If desired, racemic mixtures of the compounds may be separated so that the individual enantiomers are isolated. The separation can be carried out by methods well known in the art, such as the coupling of a racemic mixture of compounds to an enantiomerically pure compound to form a diastereomeric mixture, followed by separation of the individual diastereomers by standard methods, such as fractional crystallization or chromatography. The coupling reaction is often the formation of salts using an enantiomerically pure acid or base. The diasteromeric derivatives may then be converted to the pure enantiomers by cleavage of the added chiral residue. The racemic mixture of the compounds can also be separated directly by chromatographic methods utilizing chiral stationary phases, which methods are well known in the art. Alternatively, any enantiomer of a compound may be obtained by stereoselective synthesis using optically pure starting materials or reagents of known configuration by methods well known in the art.

The compounds of the present invention may exist in different tautomeric forms, and all such forms are embraced within the scope of the invention. Also, for example, all keto-enol, lactam-lactim and amide-imidic acid forms of the compounds are included in the invention. Thus, for example, the compounds of the invention conforming to the formula:

and their tautomers

are both contemplated as being within the scope of the compounds of the invention.

As appreciated by those of skill in the art, halogen or halo as used herein are intended to include fluoro, chloro, bromo and iodo. The term C₁₋₆, as in C₁₋₆alkyl is defined to identify the group as having 1, 2, 3, 4, 5 or 6 carbons in a linear or branched arrangement, such that C₁₋₆alkyl specifically includes methyl, ethyl, n-propyl, iso-propyl, n-butyl, iso-butyl, tert-butyl, pentyl, and hexyl. Substituents (such as R^(1a), R^(1b) and R^(1c)) may be absent if the valency of the group to which they are attached does not permit such substitution. A group which is designated as being independently substituted with substituents may be independently substituted with multiple numbers of such substituents.

The present invention also includes all pharmaceutically acceptable isotopic variations of a compound of the Formula I in which one or more atoms is replaced by atoms having the same atomic number, but an atomic mass or mass number different from the atomic mass or mass number usually found in nature. Examples of isotopes suitable for inclusion in the compounds of the invention include isotopes of hydrogen such as ²H and ³H, carbon such as ¹¹C, ¹³C and ¹⁴C, nitrogen such as ¹³N and ¹⁵N, oxygen such as ¹⁵O, ¹⁷O and ¹⁸O, phosphorus such as ³²P, sulfur such as ³⁵S, fluorine such as ¹⁸F, iodine such as ¹²³I and ¹²⁵I, and chlorine such as ³⁶Cl. Certain isotopically-labelled compounds of Formula I, for example those incorporating a radioactive isotope, are useful in drug and/or substrate tissue distribution studies. The radioactive isotopes tritium, i.e. ³H, and carbon-14, i.e. ¹⁴C, are particularly useful for this purpose in view of their ease of incorporation and ready means of detection. Substitution with heavier isotopes such as deuterium, i.e. ²H, may afford certain therapeutic advantages resulting from greater metabolic stability, for example, increased in vivo half-life or reduced dosage requirements, and hence may be preferred in some circumstances. Substitution with positron emitting isotopes, such as ¹¹C, ¹⁸F, ¹⁵O and ¹³N, can be useful in Positron Emission Topography (PET) studies for examining substrate receptor occupancy. An embodiment of the present invention includes compounds that are substituted with a positron emitting isotope. An embodiment of the present invention includes compounds that are substituted with a ¹¹C isotope. An embodiment of the present invention includes compounds that are substituted with an ¹⁸F isotope. Isotopically-labelled compounds of Formula I can generally be prepared by conventional techniques known to those skilled in the art or by processes analogous to those described in the accompanying Examples using appropriate isotopically-labelled reagents in place of the non-labelled reagent previously employed.

The term “pharmaceutically acceptable salts” refers to salts prepared from pharmaceutically acceptable non-toxic bases or acids including inorganic or organic bases and inorganic or organic acids. Salts derived from inorganic bases include aluminum, ammonium, calcium, copper, ferric, ferrous, lithium, magnesium, manganic salts, manganous, potassium, sodium, zinc, and the like. Particular embodiments include the ammonium, calcium, magnesium, potassium, and sodium salts. Salts in the solid form may exist in more than one crystal structure, and may also be in the form of hydrates or solvates. Salts derived from pharmaceutically acceptable organic non-toxic bases include salts of primary, secondary, and tertiary amines, substituted amines including naturally occurring substituted amines, cyclic amines, and basic ion exchange resins, such as arginine, betaine, caffeine, choline, N,N′-dibenzylethylene-diamine, diethylamine, 2-diethylaminoethanol, 2-dimethylaminoethanol, ethanolamine, ethylenediamine, N-ethyl-morpholine, N-ethylpiperidine, glucamine, glucosamine, histidine, hydrabamine, isopropylamine, lysine, methylglucamine, morpholine, piperazine, piperidine, polyamine resins, procaine, purines, theobromine, triethylamine, trimethylamine, tripropylamine, tromethamine, and the like.

When the compound of the present invention is basic, salts may be prepared from pharmaceutically acceptable non-toxic acids, including inorganic and organic acids. Such acids include acetic, benzenesulfonic, benzoic, camphorsulfonic, citric, ethanesulfonic, fumaric, gluconic, glutamic, hydrobromic, hydrochloric, isethionic, lactic, maleic, malic, mandelic, methanesulfonic, mucic, nitric, pamoic, pantothenic, phosphoric, succinic, sulfuric, tartaric, p-toluenesulfonic acid, and the like. Particular embodiments include the citric, hydrobromic, hydrochloric, maleic, phosphoric, sulfuric, fumaric, and tartaric acids. It will be understood that, as used herein, references to the compounds of Formula I are meant to also include the pharmaceutically acceptable salts.

Exemplifying the invention is the use of the compounds disclosed in the Examples and herein. Specific compounds within the present invention include a compound which is selected from the group consisting of the compounds disclosed in the following Examples and pharmaceutically acceptable salts thereof and individual enantiomers or diastereomers thereof.

The subject compounds may be useful in a method of treating a neurological or psychiatric disorder associated with PDE9 dysfunction in a patient such as a mammal in need of such inhibition comprising the administration of an effective amount of the compound. In addition to primates, especially humans, a variety of other mammals may be treated according to the method of the present invention. The subject compounds may be useful in a method of inhibiting PDE9 activity in a patient such as a mammal in need of such inhibition comprising the administration of an effective amount of the compound. The subject compounds are also may be useful for treating a neurological or psychiatric disorder associated with striatal hypofunction or basal ganglia dysfunction in a mammalian patient in need thereof. In addition to primates, especially humans, a variety of other mammals may be treated according to the method of the present invention.

The present invention is directed to a compound of the present invention or a pharmaceutically acceptable salt thereof for use in medicine. The present invention is further directed to a use of a compound of the present invention or a pharmaceutically acceptable salt thereof for the manufacture of a medicament for treating a neurological or psychiatric disorder associated with PDE9 dysfunction in a mammalian patient in need thereof. The present invention is further directed to a use of a compound of the present invention or a pharmaceutically acceptable salt thereof for the manufacture of a medicament for treating a neurological or psychiatric disorder associated with striatal hypofunction or basal ganglia dysfunction in a mammalian patient in need thereof.

“Treating” or “treatment of” a disease state includes: 1) preventing the disease state, i.e. causing the clinical symptoms of the disease state not to develop in a subject that may be exposed to or predisposed to the disease state, but does not yet experience or display symptoms of the disease state; 2) inhibiting the disease state, i.e., arresting the development of the disease state or its clinical symptoms; 3) or relieving the disease state, i.e., causing temporary or permanent regression of the disease state or its clinical symptoms. As used herein, the terms “treatment” and “treating” refer to all processes wherein there may be a slowing, interrupting, arresting, controlling, or stopping of the progression of the neurological and psychiatric disorders described herein, but does not necessarily indicate a total elimination of all disorder symptoms, as well as the prophylactic therapy to retard the progression or reduce the risk of the noted conditions, particularly in a patient who is predisposed to such disease or disorder.

The subject treated in the present methods is generally a mammal, in particular, a human being, male or female, in whom therapy is desired. The term “therapeutically effective amount” means the amount of the subject compound that will elicit the biological or medical response of a tissue, system, animal or human that is being sought by the researcher, veterinarian, medical doctor or other clinician. It is recognized that one skilled in the art may affect the neurological and psychiatric disorders by treating a patient presently afflicted with the disorders or by prophylactically treating a patient afflicted with such disorders with an effective amount of the compound of the present invention.

Applicants propose that inhibitors of PDE9, and in particular inhibitors of PDE9A, may provide therapeutic benefit to those individuals suffering from psychiatric and cognitive disorders. The conserved localization of PDE9 in cortex and hippocampus of rodents and humans, brain regions that play a key role in memory and learning, together with the previously described role for NO/cGMP/PKG signaling in synaptic plasticity and cognition has focused attention on a possible role for PDE9 in cognitive function and consequently as a therapeutic target for cognitive dysfunction in Alzheimer's disease and schizophrenia. The mechanism by which PDE9 inhibition improve cognitive function through the modulation of glutamate and/or cholinergic neuron signaling is potentially feasible given that both glutamate (NMDA) and cholinergic receptor activation enhance the formation of cGMP in brain and both neural substrates are involved in cognitive function.

As used herein, the term “selective PDE9 inhibitor” refers to an organic molecule that effectively inhibits an enzyme from the PDE9 family to a greater extent than enzymes from the PDE 1-8 or PDE10-11 families. In one embodiment, a selective PDE9 inhibitor is an organic molecule having a Ki for inhibition of PDE9 that is less than or about one-tenth that for a substance that is an inhibitor for another PDE enzyme. In other words, the organic molecule inhibits PDE9 activity to the same degree at a concentration of about one-tenth or less than the concentration required for any other PDE enzyme. Preferably, a selective PDE9 inhibitor is an organic molecule, having a Ki for inhibition of PDE9 that is less than or about one-hundredth that for a substance that is an inhibitor for another PDE enzyme. In other words, the organic molecule inhibits PDE9 activity to the same degree at a concentration of about one-hundredth or less than the concentration required for any other PDE enzyme. A “selective PDE9 inhibitor” can be identified, for example, by comparing the ability of an organic molecule to inhibit PDE9 activity to its ability to inhibit PDE enzymes from the other PDE families. For example, an organic molecule may be assayed for its ability to inhibit PDE9 activity, as well as PDE1A, PDE1B, PDE1C, PDE2A, PDE3A, PDE3B, PDE4A, PDE4B, PDE4C, PDE4D, PDE5A, PDE6A, PDE6B, PDE6C, PDE7A, PDE7B, PDE8A, PDE8B, PDE10A, and/or PDE11A.

Phosphodiesterase enzymes including PDE9 have been implicated in a wide range of biological functions. This has suggested a potential role for these enzymes in a variety of disease processes in humans or other species. The compounds of the present invention may have utility in treating a variety of neurological and psychiatric disorders.

In a specific embodiment, compounds of the present invention may provide a method for treating schizophrenia or psychosis comprising administering to a patient in need thereof an effective amount of a compound of the present invention. The Diagnostic and Statistical Manual of Mental Disorders (DSM-IV-TR) (2000, American Psychiatric Association, Washington D.C.) provides a diagnostic tool that includes paranoid, disorganized, catatonic or undifferentiated schizophrenia and substance-induced psychotic disorders. As used herein, the term “schizophrenia or psychosis” includes the diagnosis and classification of these mental disorders as described in DSM-IV-TR and the term is intended to include similar disorders described in other sources. Disorders and conditions encompassed herein include, but are not limited to, conditions or diseases such as schizophrenia or psychosis, including schizophrenia (paranoid, disorganized, catatonic, undifferentiated, or residual type), schizophreniform disorder, schizoaffective disorder, for example of the delusional type or the depressive type, delusional disorder, psychotic disorder, brief psychotic disorder, shared psychotic disorder, psychotic disorder due to a general medical condition and substance-induced or drug-induced (for example psychosis induced by alcohol, amphetamine, cannabis, cocaine, hallucinogens, inhalants, opioids, phencyclidine, ketamine and other dissociative anaesthetics, and other psychostimulants), psychosispsychotic disorder, psychosis associated with affective disorders, brief reactive psychosis, schizoaffective psychosis, “schizophrenia-spectrum” disorders such as schizoid or schizotypal personality disorders, personality disorder of the paranoid type, personality disorder of the schizoid type, illness associated with psychosis (such as major depression, manic depressive (bipolar) disorder, Alzheimer's disease and post-traumatic stress syndrome), including both the positive and the negative symptoms of schizophrenia and other psychoses.

In another specific embodiment, the compounds of the present invention may provide a method for treating cognitive disorders comprising administering to a patient in need thereof an effective amount of a compound of the present invention. The DSM-IV-TR also provides a diagnostic tool that includes cognitive disorders including dementia, delirium, amnestic disorders and age-related cognitive decline. As used herein, the term “cognitive disorders” includes the diagnosis and classification of these disorders as described in DSM-IV-TR and the term is intended to include similar disorders described in other sources. Disorders and conditions encompassed herein include, but are not limited to, disorders that comprise as a symptom a deficiency in attention and/or cognition, such as dementia (associated with Alzheimer's disease, ischemia, multi-infarct dementia, trauma, intracranial tumors, cerebral trauma, vascular problems or stroke, alcoholic dementia or other drug-related dementia, AIDS, HIV disease, Parkinson's disease, Huntington's disease, Pick's disease, Creutzfeldt Jacob disease, perinatal hypoxia, other general medical conditions or substance abuse), Alzheimer's disease, multi-infarct dementia, AIDS-related dementia, and Fronto temperal dementia, delirium, amnestic disorders or age related cognitive decline.

In another specific embodiment, compounds of the present invention may provide a method for treating anxiety disorders comprising administering to a patient in need thereof an effective amount of a compound of the present invention. The DSM-IV-TR also provides a diagnostic tool that includes anxiety disorders as generalized anxiety disorder, obsessive-compulsive disorder and panic attack. As used herein, the term “anxiety disorders” includes the diagnosis and classification of these mental disorders as described in DSM-IV-TR and the term is intended to include similar disorders described in other sources. Disorders and conditions encompassed herein include, but are not limited to, anxiety disorders such as, acute stress disorder, agoraphobia, generalized anxiety disorder, obsessive-compulsive disorder, panic attack, panic disorder, post-traumatic stress disorder, separation anxiety disorder, social phobia, specific phobia, substance-induced anxiety disorder and anxiety due to a general medical condition.

In another specific embodiment, compounds of the present invention may provide a method for treating substance-related disorders and addictive behaviors comprising administering to a patient in need thereof an effective amount of a compound of the present invention. The DSM-IV-TR also provides a diagnostic tool that includes persisting dementia, persisting amnestic disorder, psychotic disorder or anxiety disorder induced by substance abuse, and tolerance of, dependence on or withdrawal from substances of abuse. As used herein, the term “substance-related disorders and addictive behaviors” includes the diagnosis and classification of these mental disorders as described in DSM-IV-TR and the term is intended to include similar disorders described in other sources. Disorders and conditions encompassed herein include, but are not limited to, substance-related disorders and addictive behaviors, such as substance-induced delirium, persisting dementia, persisting amnestic disorder, psychotic disorder or anxiety disorder, drug addiction, tolerance, and dependence or withdrawal from substances including alcohol, amphetamines, cannabis, cocaine, hallucinogens, inhalants, nicotine, opioids, phencyclidine, sedatives, hypnotics or anxiolytics.

In another specific embodiment, compounds of the present invention may provide a method for treating obesity or eating disorders associated with excessive food intake, and complications associated therewith, comprising administering to a patient in need thereof an effective amount of a compound of the present invention. At present, obesity is included in the tenth edition of the International Classification of Diseases and Related Health Problems (ICD-10) (1992 World Health Organization) as a general medical condition. The DSM-IV-TR also provides a diagnostic tool that includes obesity in the presence of psychological factors affecting medical condition. As used herein, the term “obesity or eating disorders associated with excessive food intake” includes the diagnosis and classification of these medical conditions and disorders described in ICD-10 and DSM-IV-TR and the term is intended to include similar disorders described in other sources. Disorders and conditions encompassed herein include, but are not limited to, obesity, bulimia nervosa and compulsive eating disorders.

In another specific embodiment, compounds of the present invention may provide a method for treating mood and depressive disorders comprising administering to a patient in need thereof an effective amount of a compound of the present invention. As used herein, the term “mood and depressive disorders” includes the diagnosis and classification of these medical conditions and disorders described in the DSM-IV-TR and the term is intended to include similar disorders described in other sources. Disorders and conditions encompassed herein include, but are not limited to, bipolar disorders, mood disorders including depressive disorders, major depressive episode of the mild, moderate or severe type, a manic or mixed mood episode, a hypomanic mood episode, a depressive episode with atypical features, a depressive episode with melancholic features, a depressive episode with catatonic features, a mood episode with postpartum onset, post-stroke depression; major depressive disorder, dysthymic disorder, minor depressive disorder, premenstrual dysphoric disorder, post-psychotic depressive disorder of schizophrenia, a major depressive disorder superimposed on a psychotic disorder such as delusional disorder or schizophrenia, a bipolar disorder, for example, bipolar I disorder, bipolar II disorder, cyclothymic disorder, depression including unipolar depression, seasonal depression and post-partum depression, premenstrual syndrome (PMS) and premenstrual dysphoric disorder (PDD), mood disorders due to a general medical condition, and substance-induced mood disorders.

In another specific embodiment, compounds of the present invention may provide a method for treating pain comprising administering to a patient in need thereof an effective amount of a compound of the present invention. Particular pain embodiments are bone and joint pain (osteoarthritis), repetitive motion pain, dental pain, cancer pain, myofascial pain (muscular injury, fibromyalgia), perioperative pain (general surgery, gynecological), chronic pain and neuropathic pain.

In other specific embodiments, compounds of the invention may provide methods for treating other types of cognitive, learning and mental related disorders including, but not limited to, learning disorders, such as a reading disorder, a mathematics disorder, or a disorder of written expression, attention-deficit/hyperactivity disorder, age-related cognitive decline, pervasive developmental disorder including autistic disorder, attention disorders such as attention-deficit hyperactivity disorder (ADHD) and conduct disorder; an NMDA receptor-related disorder, such as autism, depression, benign forgetfulness, childhood learning disorders and closed head injury; a neurodegenerative disorder or condition, such as neurodegeneration associated with cerebral trauma, stroke, cerebral infarct, epileptic seizure, neurotoxin poisoning, or hypoglycemia-induced neurodegeneration; multi-system atrophy; movement disorders, such as akinesias and akinetic-rigid syndromes (including, Parkinson's disease, drug-induced parkinsonism, post-encephalitic parkinsonism, progressive supranuclear palsy, multiple system atrophy, corticobasal degeneration, parkinsonism-ALS dementia complex and basal ganglia calcification), medication-induced parkinsonism (such as, neuroleptic-induced parkinsonism, neuroleptic malignant syndrome, neuroleptic-induced acute dystonia, neuroleptic-induced acute akathisia, neuroleptic-induced tardive dyskinesia and medication-induced postural tremor), Huntington's disease, dyskinesia associated with dopamine agonist therapy, Gilles de la Tourette's syndrome, epilepsy, muscular spasms and disorders associated with muscular spasticity or weakness including tremors; dyskinesias, including tremor (such as, rest tremor, postural tremor, intention tremor and essential tremor), restless leg syndrome, chorea (such as Sydenham's chorea, Huntington's disease, benign hereditary chorea, neuroacanthocytosis, symptomatic chorea, drug-induced chorea and hemiballism), myoclonus (including, generalised myoclonus and focal myoclonus), tics (including, simple tics, complex tics and symptomatic tics), dystonia (including, generalised, iodiopathic, drug-induced, symptomatic, paroxymal, and focal (such as blepharospasm, oromandibular, spasmodic, spasmodic torticollis, axial dystonia, hemiplegic and dystonic writer's cramp)); urinary incontinence; neuronal damage (including ocular damage, retinopathy or macular degeneration of the eye, tinnitus, hearing impairment and loss, and brain edema); emesis; and sleep disorders, including insomnia and narcolepsy.

Of the disorders above, the treatment of schizophrenia, bipolar disorder, depression, including unipolar depression, seasonal depression and post-partum depression, premenstrual syndrome (PMS) and premenstrual dysphoric disorder (PDD), learning disorders, pervasive developmental disorders, including autistic disorder, attention disorders including Attention-Deficit/Hyperactivity Disorder, autism, tic disorders including Tourette's disorder, anxiety disorders including phobia and post traumatic stress disorder, cognitive disorders associated with dementia, AIDS dementia, Alzheimer's, Parkinson's, Huntington's disease, spasticity, myoclonus, muscle spasm, tinnitus and hearing impairment and loss are of particular importance.

The activity of the compounds in accordance with the present invention as PDE9 inhibitors may be readily determined without undue experimentation using a fluorescence polarization (FP) methodology that is well known in the art (Huang, W., et al., J. Biomol Screen, 2002, 7: 215). In particular, the compounds of the following examples had activity in reference assays by exhibiting the ability to inhibit the hydrolysis of the phosphosphate ester bond of a cyclic nucleotide.

In a typical experiment the PDE9 inhibitory activity of the compounds of the present invention was determined in accordance with the following experimental method. Rhesus PDE9A2 was amplified from rhesus whole brain cDNA (Biochain Institute) essentially as described in Hutson, et al. Neuropharmacology (2011) 61(4):665-676. HEK 293 or CHO cells over-expressing rhesus or rat PDE9A2 (created by DiscoverX from mRNA Genbank accession # NM_138543) respectively were lysed in 20 mM HEPES, 1 mM EDTA buffer with protease inhibitors (Roche, Indianapolis, Ind.). After brief homogenization, cells were pelleted via centrifugation at 75,000×g for 20 min at 4° C. The pellets were re-suspended, centrifuged and re-pelleted again in the same manner. The membrane fraction was collected in 20 mM HEPES, 1 mM MgCl2 with protease inhibitors. Human PDE9 (PDE9A2, GenBank Accession No. NM_001001567), full length with N-terminal GST tag, was purchased from BPS Bioscience. The fluorescence polarization assay for cyclic nucleotide phosphodiesterases was performed using an IMAP® FP kit supplied by Molecular Devices, Sunnyvale, Calif. (product # R8139). IMAP® technology has been applied previously to phosphodiesterase assays (Huang, W., et al., J. Biomol Screen, 2002, 7: 215). Assays were performed at room temperature in 384-well microtiter plates with an incubation volume of 20.2 μL. Solutions of test compounds were prepared in DMSO and serially diluted with DMSO to yield 8 μL of each of 10 solutions differing by 3-fold in concentration, at 32 serial dilutions per plate. 100% inhibition is determined using a known PDE9 inhibitor, such as 1-(2-chlorophenyl)-6-[(2R)-3,3,3-trifluoro-2-methylpropyl]-1,5-dihydro-4H-pyrazolo[3,4-d]pyrimidine-4-one (BAY 73-6691) (Wunder et al, Mol. Pharmacol., 2005, 68(6): 1775-81), (6-[(3S,4S)-4-methyl-1-(pyrimidin-2-ylmethyl)pyrrolidin-3-yl]-1-(tetrahydro-2H-pyran-4-yl)-1,5-dihydro-4H-pyrazolo[3,4-d]pyrimidin-4-one (PF-04447943) (Wager et al., ACS Chemical Neuroscience, 2010, 1:435-449). 0% of inhibition is determined by using DMSO (1% final concentrations). A Labcyte Echo 555 (Labcyte, Sunnyvale, Calif.) is used to dispense 200 nL from each well of the titration plate to the 384 well assay plate. Rhesus membrane preps were diluted to 4 ng/ml, rat membrane preps diluted to 13 ng/ml, and human PDE9A2 diluted to 1 ng/ml. FAM-labeled cGMP substrate (Molecular Devices, Sunnyvale, Calif.) was at a concentration of 100 nM (Km of PDE9 for cGMP is 70-170 nM) in the assay buffer (10 mM Tris HCl, pH 7.2, 10 mM MgCl₂, 0.05% NaN₃ 0.01% Tween-20, and 1 mM DTT). PDE9 enzyme mix and compounds were mixed and incubated at room temperature for 30 min. Following which, FAMcGMP substrate was added, shaken and incubated for an additional 60 min at room temperature. The final concentrations of rhesus and rat membrane preparations were 2 ng/ml and 6.5 ng/ml, respectively, while the human PDE9 was used at a final concentration of 0.5 ng/ml. The final concentration of FAM-cGMP was 50 nM. After the incubation period, the enzymatic reaction was stopped by addition of binding solution (IMAP-FP, Molecular Devices, comprised of 80% Solution A, 20% Solution B and a 1:600 dilution of binding reagent) to each well. The plates were shaken then incubated at room temperature for 1 h prior to determining the fluorescence polarization (mP) using a Perkin Elmer EnVision™ plate reader (Waltham, Mass.).

Fluorescence polarization (mP) was calculated from the parallel (S) and perpendicular (P) fluorescence of each sample well and the analogous values for the median control well, containing only substrate (So and Po), using the following equation: Polarization (mP)=1000*(S/So−P/Po)/(S/So+P/Po).

Dose-inhibition profiles for each compound were characterized by fitting the mP data to a four-parameter equation given below. The apparent inhibition constant (K_(I)), the maximum inhibition at the low plateau relative to “100% Inhibition Control” (Imax; e.g. 1=>same as this control), the minimum inhibition at the high plateau relative to the “0% Inhibition Control” (Imin, e.g. 0=>same as the no drug control) and the Hill slope (nH) are determined by a non-linear least squares fitting of the mP values as a function of dose of the compound using an in-house software based on the procedures described by Mosser et al., JALA, 2003, 8: 54-63, using the following equation:

${mP} = {\frac{\left( {{0\% \mspace{14mu} {mP}} - {100\% \mspace{14mu} {mP}}} \right)\left( {{I\; \max} - {I\; \min}} \right)}{1 + \left\lbrack \frac{\lbrack{Drug}\rbrack}{\left( {10^{- {pK}_{I}}\left( {1 + \frac{\lbrack{Substrate}\rbrack}{K_{M}}} \right)} \right.} \right\rbrack^{nH}} + {100\% \mspace{14mu} {mP}} + {\left( {{0\% \mspace{14mu} {mP}} - {100\% \mspace{14mu} {mP}}} \right)\left( {1 - {I\; \max}} \right)}}$

The median signal of the “0% inhibition controls” (0% mP) and the median signal of the “100% inhibition controls” (100% mP) are constants determined from the controls located in columns 1-2 and 23-24 of each assay plate. An apparent (K_(m)) for FAM-labeled cAMP of 150 nM was determined in separate experiments through simultaneous variation of substrate and selected drug concentrations.

Selectivity for PDE9, as compared to other PDE families, was assessed using the IMAP® technology. Rhesus PDE2A3 and Human PDE10A2 enzyme was prepared from cytosolic fractions of transiently transfected HEK cells. All other PDE's were GST Tag human enzyme expressed in insect cells and were obtained from BPS Bioscience (San Diego, Calif.): PDE1A (Cat#60010), PDE3A (Cat#60030), PDE4A1A (Cat#60040), PDE5A1 (Cat#60050), PDE6C (Cat#60060), PDE7A (Cat#60070), PDE8A1 (Cat#60080), PDE9A2 (Cat#60090), PDE11A4 (Cat#60110).

Assays for PDE 1 through 11 were performed in parallel at room temperature in 384-well microtiter plates with an incubation volume of 20.2 μL. Solutions of test compounds were prepared in DMSO and serially diluted with DMSO to yield 30 μL of each of ten solutions differing by 3-fold in concentration, at 32 serial dilutions per plate. 100% inhibition was determined by adding buffer in place of the enzyme and 0% inhibition is determined by using DMSO (1% final concentrations). A Labcyte POD 810 (Labcyte, Sunnyvale, Calif.) was used to dispense 200 nL from each well of the titration plate to make eleven copies of the assay plate for each titration, one copy for each PDE enzyme. A solution of each enzyme (dilution from aliquots, sufficient to produce 20% substrate conversion) and a separate solution of FAM-labeled cAMP or FAM-labeled cGMP from Molecular Devices (Sunnyvale, Calif., product # R7506 or cGMP#R7508), at a final concentration of 50 nM were made in the assay buffer (10 mM Tris HCl, pH 7.2, 10 mM MgCl₂, 0.05% NaN₃ 0.01% Tween-20, and 1 mM DTT). Note that the substrate for PDE2 is 50 nM FAM cAMP containing 1000 nM of cGMP. The enzyme and the substrate were then added to the assay plates in two consecutive additions of 10 μL and then shaken to mix. The reaction was allowed to proceed at room temperature for 60 minutes. A binding solution was then made from the kit components, comprised of 80% Solution A, 20% Solution B and binding reagent at a volume of 1/600 the total binding solution. The enzymatic reaction was stopped by addition of 60 μL of the binding solution to each well of the assay plate. The plates were sealed and shaken for 10 seconds. The plates were incubated at room temperature for one hour. The parallel and perpendicular fluorescence of each well of the plate was measured using a Perkin Elmer EnVision™ plate reader (Waltham, Mass.). The apparent inhibition constants for the compounds against all 11 PDE's was determined from the parallel and perpendicular fluorescent readings as described for PDE FP assay using the following apparent K_(M) values for each enzyme and substrate combination: PDE1A (FAM cGMP) 70 nM, rhesus PD2A3 (FAM cAMP) 10,000 nM, PDE3A (FAM cAMP) 50 nM, PDE4A1A (FAM cAMP) 1500 nM, PDE5A1 (FAM cGMP) 400 nM, PDE6C (FAM cGMP) 700 nM, PDE7A (FAM cAMP) 150 nM, PDE8A1 (FAM cAMP) 50 nM, PDE10A2 (FAM cAMP) 150 nM, PDE11A4 (FAM cAMP) 1000 nM. The intrinsic PDE10 inhibitory activity of a compound which may be used in accordance with the present invention may be determined by these assays.

The compounds of the following examples had activity in inhibiting the human PDE9 enzyme in the aforementioned assays, generally with a Ki of less than about 1 μM. Many of compounds within the present invention had activity in inhibiting the human PDE9 enzyme in the aforementioned assays, generally with a Ki of less than about 0.1 μM. Additional data are provided in the following Examples. Such a result is indicative of the intrinsic activity of the compounds in use as inhibitors of the PDE9 enzyme. In general, one of ordinary skill in the art would appreciate that a substance is considered to effectively inhibit PDE9 activity if it has a Ki of less than or about 5 μM, where more potent inhibitors have a Ki of less than or about 0.1 μM. The present invention also includes compounds within the scope of the invention which possess activity as inhibitors of other phosphodiesterase enzymes.

The subject compounds may be further useful in a method for the prevention, treatment, control, amelioration, or reduction of risk of the diseases, disorders and conditions noted herein. The subject compounds may be further useful in a method for the prevention, treatment, control, amelioration, or reduction of risk of the aforementioned diseases, disorders and conditions in combination with other agents. The compounds of the present invention may be used in combination with one or more other drugs in the treatment, prevention, control, amelioration, or reduction of risk of diseases or conditions for which compounds of the present invention or the other drugs may have utility, where the combination of the drugs together are safer or more effective than either drug alone. Such other drug(s) may be administered, by a route and in an amount commonly used therefore, contemporaneously or sequentially with a compound of the present invention. When a compound of the present invention is used contemporaneously with one or more other drugs, a pharmaceutical composition in unit dosage form containing such other drugs and the compound of the present invention may be desirable. However, the combination therapy may also include therapies in which the compound of the present invention and one or more other drugs are administered on different overlapping schedules. It is also contemplated that when used in combination with one or more other active ingredients, the compounds of the present invention and the other active ingredients may be used in lower doses than when each is used singly. Accordingly, the pharmaceutical compositions of the present invention include those that contain one or more other active ingredients, in addition to a compound of the present invention. The above combinations include combinations of a compound of the present invention not only with one other active compound, but also with two or more other active compounds. Likewise, compounds of the present invention may be used in combination with other drugs that are used in the prevention, treatment, control, amelioration, or reduction of risk of the diseases or conditions for which compounds of the present invention are useful. Such other drugs may be administered, by a route and in an amount commonly used therefore, contemporaneously or sequentially with a compound of the present invention. Accordingly, the pharmaceutical compositions of the present invention include those that also contain one or more other active ingredients, in addition to a compound of the present invention. The weight ratio of the compound of the present invention to the second active ingredient may be varied and will depend upon the effective dose of each ingredient. Generally, an effective dose of each will be used. Thus, for example, when a compound of the present invention is combined with another agent, the weight ratio of the compound of the present invention to the other agent will generally range from about 1000:1 to about 1:1000, such as about 200:1 to about 1:200. Combinations of a compound of the present invention and other active ingredients will generally also be within the aforementioned range, but in each case, an effective dose of each active ingredient should be used.

In such combinations the compound of the present invention and other active agents may be administered separately or in conjunction. In addition, the administration of one element may be prior to, concurrent to, or subsequent to the administration of other agent(s).

Accordingly, the subject compounds may be used alone or in combination with other agents which are known to be beneficial in the subject indications or other drugs that affect receptors or enzymes that either increase the efficacy, safety, convenience, or reduce unwanted side effects or toxicity of the compounds of the present invention. The subject compound and the other agent may be co-administered, either in concomitant therapy or in a fixed combination.

In one embodiment, the subject compound may be employed in combination with anti-Alzheimer's agents, beta-secretase inhibitors, gamma-secretase inhibitors, HMG-CoA reductase inhibitors, NSAID's including ibuprofen, vitamin E, and anti-amyloid antibodies.

In another embodiment, the subject compound may be employed in combination with sedatives, hypnotics, anxiolytics, antipsychotics, antianxiety agents, cyclopyrrolones, imidazopyridines, pyrazolopyrimidines, minor tranquilizers, melatonin agonists and antagonists, melatonergic agents, benzodiazepines, barbiturates, 5HT-2 antagonists, and the like, such as: adinazolam, allobarbital, alonimid, alprazolam, amisulpride, amitriptyline, amobarbital, amoxapine, aripiprazole, atypical antipsychotics, bentazepam, benzoctamine, brotizolam, bupropion, busprione, butabarbital, butalbital, capuride, carbocloral, chloral betaine, chloral hydrate, clomipramine, clonazepam, cloperidone, clorazepate, chlordiazepoxide, clorethate, chlorpromazine, clozapine, cyprazepam, desipramine, dexclamol, diazepam, dichloralphenazone, divalproex, diphenhydramine, doxepin, estazolam, ethchlorvynol, etomidate, fenobam, flunitrazepam, flupentixol, fluphenazine, flurazepam, fluvoxamine, fluoxetine, fosazepam, glutethimide, halazepam, haloperidol, hydroxyzine, imipramine, lithium, lorazepam, lormetazepam, maprotiline, mecloqualone, melatonin, mephobarbital, meprobamate, methaqualone, midaflur, midazolam, nefazodone, nisobamate, nitrazepam, nortriptyline, olanzapine, oxazepam, paraldehyde, paroxetine, pentobarbital, perlapine, perphenazine, phenelzine, phenobarbital, prazepam, promethazine, propofol, protriptyline, quazepam, quetiapine, reclazepam, risperidone, roletamide, secobarbital, sertraline, suproclone, temazepam, thioridazine, thiothixene, tracazolate, tranylcypromaine, trazodone, triazolam, trepipam, tricetamide, triclofos, trifluoperazine, trimetozine, trimipramine, uldazepam, venlafaxine, zaleplon, ziprasidone, zolazepam, zolpidem, and salts thereof, and combinations thereof, and the like, or the subject compound may be administered in conjunction with the use of physical methods such as with light therapy or electrical stimulation.

In another embodiment, the subject compound may be employed in combination with levodopa (with or without a selective extracerebral decarboxylase inhibitor such as carbidopa or benserazide), anticholinergics such as biperiden (optionally as its hydrochloride or lactate salt) and trihexyphenidyl (benzhexol) hydrochloride, COMT inhibitors such as entacapone, MOA-B inhibitors, antioxidants, A2a adenosine receptor antagonists, cholinergic agonists, NMDA receptor antagonists, serotonin receptor antagonists and dopamine receptor agonists such as alentemol, bromocriptine, fenoldopam, lisuride, naxagolide, pergolide and pramipexole. It will be appreciated that the dopamine agonist may be in the form of a pharmaceutically acceptable salt, for example, alentemol hydrobromide, bromocriptine mesylate, fenoldopam mesylate, naxagolide hydrochloride and pergolide mesylate. Lisuride and pramipexol are commonly used in a non-salt form.

In another embodiment, the subject compound may be employed in combination with a compound from the phenothiazine, thioxanthene, heterocyclic dibenzazepine, butyrophenone, diphenylbutylpiperidine and indolone classes of neuroleptic agent. Suitable examples of phenothiazines include chlorpromazine, mesoridazine, thioridazine, acetophenazine, fluphenazine, perphenazine and trifluoperazine. Suitable examples of thioxanthenes include chlorprothixene and thiothixene. An example of a dibenzazepine is clozapine. An example of a butyrophenone is haloperidol. An example of a diphenylbutylpiperidine is pimozide. An example of an indolone is molindolone. Other neuroleptic agents include loxapine, sulpiride and risperidone. It will be appreciated that the neuroleptic agents when used in combination with the subject compound may be in the form of a pharmaceutically acceptable salt, for example, chlorpromazine hydrochloride, mesoridazine besylate, thioridazine hydrochloride, acetophenazine maleate, fluphenazine hydrochloride, flurphenazine enathate, fluphenazine decanoate, trifluoperazine hydrochloride, thiothixene hydrochloride, haloperidol decanoate, loxapine succinate and molindone hydrochloride. Perphenazine, chlorprothixene, clozapine, haloperidol, pimozide and risperidone are commonly used in a non-salt form. Thus, the subject compound may be employed in combination with acetophenazine, alentemol, aripiprazole, amisulpride, benzhexol, bromocriptine, biperiden, chlorpromazine, chlorprothixene, clozapine, diazepam, fenoldopam, fluphenazine, haloperidol, levodopa, levodopa with benserazide, levodopa with carbidopa, lisuride, loxapine, mesoridazine, molindolone, naxagolide, olanzapine, pergolide, perphenazine, pimozide, pramipexole, quetiapine, risperidone, sulpiride, tetrabenazine, trihexyphenidyl, thioridazine, thiothixene, trifluoperazine or ziprasidone.

In another embodiment, the subject compound may be employed in combination with an anti-depressant or anti-anxiety agent, including norepinephrine reuptake inhibitors (including tertiary amine tricyclics and secondary amine tricyclics), selective serotonin reuptake inhibitors (SSRIs), monoamine oxidase inhibitors (MAOIs), reversible inhibitors of monoamine oxidase (RIMAs), serotonin and noradrenaline reuptake inhibitors (SNRIs), corticotropin releasing factor (CRF) antagonists, α-adrenoreceptor antagonists, neurokinin-1 receptor antagonists, atypical anti-depressants, benzodiazepines, 5-HT_(1A) agonists or antagonists, especially 5-HT_(1A) partial agonists, and corticotropin releasing factor (CRF) antagonists. Specific agents include: amitriptyline, clomipramine, doxepin, imipramine and trimipramine; amoxapine, desipramine, maprotiline, nortriptyline and protriptyline; fluoxetine, fluvoxamine, paroxetine and sertraline; isocarboxazid, phenelzine, tranylcypromine and selegiline; moclobemide: venlafaxine; duloxetine; aprepitant; bupropion, lithium, nefazodone, trazodone and viloxazine; alprazolam, chlordiazepoxide, clonazepam, chlorazepate, diazepam, halazepam, lorazepam, oxazepam and prazepam; buspirone, flesinoxan, gepirone and ipsapirone, and pharmaceutically acceptable salts thereof.

The compounds of the present invention may be administered by oral, parenteral (e.g., intramuscular, intraperitoneal, intravenous, ICV, intracisternal injection or infusion, subcutaneous injection, or implant), by inhalation spray, nasal, vaginal, rectal, sublingual, or topical routes of administration and may be formulated, alone or together, in suitable dosage unit formulations containing conventional non-toxic pharmaceutically acceptable carriers, adjuvants and vehicles appropriate for each route of administration. In addition to the treatment of warm-blooded animals such as mice, rats, horses, cattle, sheep, dogs, cats, monkeys, etc., the compounds of the invention are effective for use in humans. The terms “administration of” and or “administering a” compound should be understood to mean providing a compound of the invention or a prodrug of a compound of the invention to the individual in need of treatment.

The term “composition” as used herein is intended to encompass a product comprising specified ingredients in predetermined amounts or proportions, as well as any product which results, directly or indirectly, from combination of the specified ingredients in the specified amounts. Such term in relation to pharmaceutical composition, is intended to encompass a product comprising the active ingredient(s), and the inert ingredient(s) that make up the carrier, as well as any product which results, directly or indirectly, from combination, complexation or aggregation of any two or more of the ingredients, or from dissociation of one or more of the ingredients, or from other types of reactions or interactions of one or more of the ingredients. In general, pharmaceutical compositions are prepared by uniformly and intimately bringing the active ingredient into association with a liquid carrier or a finely divided solid carrier or both, and then, if necessary, shaping the product into the desired formulation. In the pharmaceutical composition the active object compound is included in an amount sufficient to produce the desired effect upon the process or condition of diseases. Accordingly, the pharmaceutical compositions of the present invention encompass any composition made by mixing a compound of the present invention and a pharmaceutically acceptable carrier.

Pharmaceutical compositions intended for oral use may be prepared according to any method known to the art for the manufacture of pharmaceutical compositions and such compositions may contain one or more agents selected from the group consisting of sweetening agents, flavoring agents, coloring agents and preserving agents in order to provide pharmaceutically elegant and palatable preparations. Tablets contain the active ingredient in admixture with non-toxic pharmaceutically acceptable excipients that are suitable for the manufacture of tablets. The tablets may be uncoated or they may be coated by known techniques to delay disintegration and absorption in the gastrointestinal tract and thereby provide a sustained action over a longer period. Compositions for oral use may also be presented as hard gelatin capsules wherein the active ingredients are mixed with an inert solid diluent, for example, calcium carbonate, calcium phosphate or kaolin, or as soft gelatin capsules wherein the active ingredient is mixed with water or an oil medium, for example peanut oil, liquid paraffin, or olive oil. Aqueous suspensions, oily suspensions, dispersible powders or granules, oil-in-water emulsions, and sterile injectable aqueous or oleagenous suspension may be prepared by standard methods known in the art. By “pharmaceutically acceptable” it is meant the carrier, diluent or excipient must be compatible with the other ingredients of the formulation and not deleterious to the recipient thereof.

The subject compounds may be further useful in a method for the prevention, treatment, control, amelioration, or reduction of risk of the diseases, disorders and conditions noted herein. The dosage of active ingredient in the compositions of this invention may be varied, however, it is necessary that the amount of the active ingredient be such that a suitable dosage form is obtained. The active ingredient may be administered to patients (animals and human) in need of such treatment in dosages that will provide optimal pharmaceutical efficacy. The selected dosage depends upon the desired therapeutic effect, on the route of administration, and on the duration of the treatment. The dose will vary from patient to patient depending upon the nature and severity of disease, the patient's weight, special diets then being followed by a patient, concurrent medication, and other factors which those skilled in the art will recognize. Generally, dosage levels of between 0.001 to 10 mg/kg. of body weight daily are administered to the patient, e.g., humans and elderly humans. The dosage range will generally be about 0.5 mg to 1.0 g. per patient per day which may be administered in single or multiple doses. In one embodiment, the dosage range will be about 0.5 mg to 500 mg per patient per day; in another embodiment about 0.5 mg to 200 mg per patient per day; and in yet another embodiment about 5 mg to 50 mg per patient per day. Pharmaceutical compositions of the present invention may be provided in a solid dosage formulation such as comprising about 0.5 mg to 500 mg active ingredient, or comprising about 1 mg to 250 mg active ingredient. The pharmaceutical composition may be provided in a solid dosage formulation comprising about 1 mg, 5 mg, 10 mg, 25 mg, 50 mg, 100 mg, 200 mg or 250 mg active ingredient. For oral administration, the compositions may be provided in the form of tablets containing 1.0 to 1000 milligrams of the active ingredient, such as 1, 5, 10, 15, 20, 25, 50, 75, 100, 150, 200, 250, 300, 400, 500, 600, 750, 800, 900, and 1000 milligrams of the active ingredient for the symptomatic adjustment of the dosage to the patient to be treated. The compounds may be administered on a regimen of 1 to 4 times per day, such as once or twice per day.

Several methods for preparing the compounds of this invention are illustrated in the following Schemes and Examples. Starting materials and the requisite intermediates are in some cases commercially available, or can be prepared according to literature procedures or as illustrated herein. The compounds of this invention may be prepared by employing reactions as shown in the following schemes, in addition to other standard manipulations that are known in the literature or exemplified in the experimental procedures. Substituent numbering as shown in the schemes does not necessarily correlate to that used in the claims and often, for clarity, a single substituent is shown attached to the compound where multiple substituents are allowed under the definitions hereinabove. Reactions used to generate the compounds of this invention are prepared by employing reactions as shown in the schemes and examples herein, in addition to other standard manipulations such as ester hydrolysis, cleavage of protecting groups, etc., as may be known in the literature or exemplified in the experimental procedures. Starting materials are made according to procedures known in the art or as illustrated herein. The following abbreviations are used herein: Me: methyl; Et: ethyl; t-Bu: tert-butyl; Ar: aryl; Ph: phenyl; Bn: benzyl; Ac: acetyl; THF: tetrahydrofuran; Boc: tert-butyloxycarbonyl; DIPEA: N,N-diisopropylethylamine; DPPA: diphenylphosphorylazide; EDC: N-(3-Dimethylaminopropyl)-N′-ethylcarbodiimide; EtOAc: ethyl acetate; HOBt: hydroxybenzotriazole hydrate; TEA: triethylamine; DMF: N,N-dimethylformamide; rt: room temperature; HPLC: high performance liquid chromatography; NMR: nuclear magnetic resonance; TLC: thin-layer chromatography.

The compounds of the present invention can be prepared in a variety of fashions. In some cases the final product may be further modified, for example, by manipulation of substituents. These manipulations may include, but are not limited to, reduction, oxidation, alkylation, acylation, and hydrolysis reactions which are commonly known to those skilled in the art. In some cases the order of carrying out the foregoing reaction schemes may be varied to facilitate the reaction or to avoid unwanted reaction products. The following examples are provided so that the invention might be more fully understood. These examples are illustrative only and should not be construed as limiting the invention in any way.

According to the general synthetic scheme 1 above, appropriately substituted 2H-benzo[d][1,3]-oxazine-2,4(1H)-diones A-1 can be reacted with ethyl 2-cyanoacetate A-2 to give 4-hydroxy-2-oxo-1,2-dihydroquinoline-3-carbonitrile A-3. Chlorination of A-3 with a POCl₃ and PCI₅ mixture yields substituted 2,4-dichloroquinoline-3-carbonitriles such as A-4. Selective acid hydrolysis of the 2-Cl with TFA in water produces key intermediate 4-chloro-2-oxo-1,2-dihydroquinoline-3-carbonitrile A-5, which can then undergo nucleophilic displacement by amines A-6 to give products of general structure A-7.

EXAMPLES

Example compounds of the present invention can be synthesized according to the schemes and procedures outlined below. Because the schemes are an illustration, the invention should not be construed as being limited by the chemical reactions and conditions expressed. The preparation of the various starting materials used in the schemes is within the skill of a person versed in the art. Absolute stereochemistry of separate stereoisomers in the examples and intermediates was not determined unless stated otherwise in an example.

Example 1

(R)-4-(3-(1H-pyrazol-1-yl)pyrrolidin-1-yl)-2-oxo-1,2-dihydroquinoline-3-carbonitrile (1-7) 2,4-dihydroxyquinoline-3-carbonitrile (1-3)

To a round bottom flask, 2H-3,1-benzoxazine-2,4(1H)-dione (Aldrich, 82 g, 503 mmol) was added and dissolved in DMF (300 ml). Ethyl cyanoacetate 1-3 (62.5 g, 533 mmol) was then added slowly and the reaction was heated to 100° C. for 5 hours, at which point it was allowed to cool and poured into H₂O. The H₂O layer was acidified to pH 1 with 0.5M aqueous HCl, the precipitated solid was filtered and dried to give 2,4-dihydroxyquinoline-3-carbonitrile (1-3), HRMS (M+H)⁺: observed=187.1, calculated=187.1

2,4-dichloroquinoline-3-carbonitrile (1-4)

2H-3,1-benzoxazine-2,4(1H)-dione (1-3) (11.9 g, 63.8 mmol), POCl₃ (44.0 g, 287 mmol) and POCl₅ (26.6 g, 128 mmol) were added to a round bottomed flask and stirred at 100° C. for 2 hours. Upon completion, the reaction mixture was allowed to cool and slowly poured over ice mixture while stirring vigorusly. The precipitate was filtered off to give a yellowish solid of 2,4-dichloroquinoline-3-carbonitrile (1-4), HRMS (M+H)⁺: observed=224.0, calculated=224.058

4-chloro-2-oxo-1,2-dihydroquinoline-3-carbonitrile (1-5)

In a round-bottomed flask, 2,4-dichloroquinoline-3-carbonitrile (1-4) (15 g, 67.2 mmol), was dissolved in 40 ml of a 4:1 mixture of TFA and H₂O. The reaction mixture was heated to 100° C. for 1 hour, then allowed to cool and poured into methanol. The precipitate was filtered off and dried to give 4-chloro-2-oxo-1,2-dihydroquinoline-3-carbonitrile (1-4) HRMS (M+H)⁺: observed=205.1, calculated=205.6

(R)-4-(3-[1H-pyrazol-1-yl]pyrrolidin-1-yl)-2-oxo-1,2-dihydroquinoline-3-carbonitrile (1-7)

4-Chloro-2-oxo-1,2-dihydroquinoline-3-carbonitrile (1-5) (20 g, 98 mmol), 1-pyrrolidine-3-yl-1H-pyrazole hydrochloride (23.8 g, 137 mmol), DIPEA (68.3 mL, 391 mmol), and DMF (244 mL) were heated to 100° C. for thirty minutes. The reaction was cooled and partitioned between water and EtOAc, and the aqueous layer was extracted with EtOAc (×3). The combined organic layers were concentrated, and the residue slurried in water to result in a brown solid which was collected by filtration. The mother liquor was aged overnight and the resulting additional brown material was collected by filtration. The combined solids were purified by SCF method (55% CO2, 45% MeOH, IA column with 0.1% DEA additive), and the second peak (6.55 min.) collected to give the single enantiomer (R)-4-(3-[1H-pyrazol-1-yl]pyrrolidin-1-yl)-2-oxo-1,2-dihydroquinoline-3-carbonitrile (1-7) as a beige solid (9.1 g, 31%). ¹H NMR (500 MHz, CD₃OD): δ 8.09 (m, 1H); 7.78 (m, 1H); 7.51-7.59 (m, 2H); 7.25 (m, 1H); 7.19 (m, 1H); 6.33 (m, 1H); 5.18 (m, 1H); 4.58 (m, 1H); 4.44 (m, 1H); 4.40 (m, 1H); 4.29 (m, 1H); 2.53 (m, 2H). MS (M+H)⁺: observed=306.08, calculated=306.334

TABLE 1 The following compounds were prepared according to the general procedure provided in the examples and procedures herein using known or prepared starting materials, as described in the reaction schemes and examples herein. The requisite starting materials are either prepared as described in the intermediates section, commercially available, or may be prepared from commercially available reagents using conventional reactions well known in the art without undue experimentation. Example Structure Name MS (M + 1) 1-8

4-(azepan-1-yl)-2- oxo-1,2- dihydroquinoline-3- carbonitrile HRMS m/z (M + H) 268.2 found, 268.3 required. 1-9

4-(azetidin-1-yl)-2- oxo-1,2- dihydroquinoline-3- carbonitrile LRMS m/z (M + H) 226 found, 226 required. 1-10

4-(diethylamino)-2- oxo-1,2- dihydroquinoline-3- carbonitrile LRMS m/z (M + H) 242.31 found, 241.29 required. 1-11

4-(4,4- dimethylpiperidin-1- yl)-2-oxo-1,2- dihydroquinoline-3- carbonitrile LRMS m/z (M + H) 282.34 found, 282.35 required. 1-12

4-((2-(oxetan-3- yl)ethyl)amino)-2- oxo-1,2- dihydroquinoline-3- carbonitrile HRMS m/z (M + H) 270.3, found, 270.3 required.

TABLE 2 The following table shows representative data for the compounds of the Examples as PDE9 inhibitors as determined by the assays described herein. In this table, the PDE9 K_(i) is a measure of the ability of the test compound to inhibit the action of the PDE9 enzyme. Such results are indicative of the intrinsic activity of the compounds for use as inhibitors of the PDE9 enzyme. Example PDE9 IMAP Ki (nM) 1-7 7.5 1-8 18 1-9 5546 1-10 88.9 1-11 26.3 1-12 71.1

While the invention has been described and illustrated with reference to certain particular embodiments thereof, those skilled in the art will appreciate that various adaptations, changes, modifications, substitutions, deletions, or additions of procedures and protocols may be made without departing from the spirit and scope of the invention. 

1. A compound of the formula I, or a pharmaceutically acceptable salt thereof:

wherein: R⁵ is selected from the group consisting of: (1) hydrogen, and (2) —C₁₋₆alkyl; R⁶ is —C₁₋₆alkyl, which is unsubstituted or substituted with oxetane; or R⁵ and R⁶ are joined together with a —C₃₋₆alkyl through the nitrogen atom to which they are attached to form a azetidine, pyrrolidine, piperidine, or azepan ring, which is unsubstituted or substituted with pyrazole or one or two —C₁₋₆alkyl; with the proviso that the compound is other than: (R)-4-(3-(1H-pyrazol-1-yl)pyrrolidin-1-yl)-2-oxo-1,2-dihydroquinoline-3-carbonitrile; or 4-(azepan-1-yl)-2-oxo-1,2-dihydroquinoline-3-carbonitrile.
 2. The compound of claim 1 wherein R⁵ is selected from the group consisting of: hydrogen and ethyl.
 3. The compound of claim 1 wherein R⁶ is ethyl, which is unsubstituted or substituted with oxetane.
 4. The compound of claim 1 wherein R⁵ and R⁶ are joined together with a —C₃₋₆alkyl through the nitrogen atom to which they are attached to form a azetidine, pyrrolidine, piperidine, or azepan ring, which is unsubstituted or substituted with pyrazole or one or two —C₁₋₆alkyl.
 5. A compound which is selected from the group consisting of: 4-(azetidin-1-yl)-2-oxo-1,2-dihydroquinoline-3-carbonitrile; 4-(diethylamino)-2-oxo-1,2-dihydroquinoline-3-carbonitrile; 4-(4,4-dimethylpiperidin-1-yl)-2-oxo-1,2-dihydroquinoline-3-carbonitrile; and 4-((2-(oxetan-3-yl)ethyl)amino)-2-oxo-1,2-dihydroquinoline-3-carbonitrile; or a pharmaceutically acceptable salt thereof.
 6. A pharmaceutical composition which comprises an inert carrier and a compound of claim 1 or a pharmaceutically acceptable salt thereof.
 7. (canceled)
 8. (canceled)
 9. A method for treating a neurological or psychiatric disorder associated with PDE9 dysfunction in a mammalian patient in need thereof which comprises administering to the patient a therapeutically effective amount of a compound of claim 1 or a pharmaceutically acceptable salt thereof.
 10. A method for treating bipolar disorder, anxiety, schizophrenia, neurological or psychiatric disorder associated with striatal hypofunction or basal ganglia dysfunction in a mammalian patient in need thereof which comprises administering to the patient a therapeutically effective amount of a compound of claim 1 or a pharmaceutically acceptable salt thereof.
 11. A method for treating Huntington's disease in a mammalian patient in need thereof which comprises administering to the patient a therapeutically effective amount of a compound of any of claim 1 or a pharmaceutically acceptable salt thereof.
 12. A method for enhancing cognition in a mammalian patient in need thereof which comprises administering to the patient a therapeutically effective amount of a compound of claim 1 or a pharmaceutically acceptable salt thereof. 